U.S. patent application number 10/779053 was filed with the patent office on 2005-08-18 for wireless diversity receiver with shared receive path.
Invention is credited to Sahota, Gurkanwal Singh.
Application Number | 20050181752 10/779053 |
Document ID | / |
Family ID | 34838299 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050181752 |
Kind Code |
A1 |
Sahota, Gurkanwal Singh |
August 18, 2005 |
Wireless diversity receiver with shared receive path
Abstract
A low-cost diversity receiver includes two receiver units for a
primary path and a secondary/diversity path. The first receiver
unit is compliant with, for example, IS-98D requirements. The
second receiver unit is not fully compliant with the IS-98D
requirements (e.g., may meet requirements for sensitivity but not
for out-of-band rejection). The second receiver unit is wideband
and designed with lower power consumption, less area, and lower
cost than the first receiver unit. For a multi-antenna receiver,
the two receiver units are used to simultaneously process two
received signals from two antennas. For a single-antenna receiver,
one of the two receiver units is used to process a received signal
from one antenna. For a dual-band design, each receiver unit can
operate at two frequency bands. Narrowband circuit blocks are used
for the first receiver unit, and wideband circuit blocks are used
for the second receiver unit.
Inventors: |
Sahota, Gurkanwal Singh;
(San Diego, CA) |
Correspondence
Address: |
Qualcomm Incorporated
Patents Department
5775 Morehouse Drive
San Diego
CA
92121-1714
US
|
Family ID: |
34838299 |
Appl. No.: |
10/779053 |
Filed: |
February 12, 2004 |
Current U.S.
Class: |
455/132 ;
455/180.1; 455/188.1; 455/552.1 |
Current CPC
Class: |
Y02D 30/70 20200801;
Y02D 70/122 20180101; Y02D 70/1262 20180101; H04B 7/0837 20130101;
Y02D 70/444 20180101; Y02D 70/164 20180101; Y02D 70/142 20180101;
H04B 7/0802 20130101; Y02D 70/144 20180101 |
Class at
Publication: |
455/132 ;
455/552.1; 455/180.1; 455/188.1 |
International
Class: |
H04B 001/00; H04B
017/02; H04B 001/18 |
Claims
What is claimed is:
1. A wireless device comprising: a first receiver unit operable to
receive and amplify first and second input signals for first and
second frequency bands to obtain first and second amplified
signals, respectively, and to downconvert the first and second
amplified signals from radio frequency (RF) to baseband and provide
first and second baseband signals, respectively; and a second
receiver unit operable to receive and amplify a third input signal
for the first or second frequency band to obtain a third amplified
signal, and to downconvert the third amplified signal from RF to
baseband and provide a third baseband signal, wherein the second
receiver unit includes at least one RF circuit block that is shared
by the first and second frequency bands.
2. The device of claim 1, wherein the second receiver unit includes
a wideband frequency downconverter that is shared by the first and
second frequency bands.
3. The device of claim 1, wherein the second receiver unit includes
a wideband variable gain amplifier (VGA) that is shared by the
first and second frequency bands.
4. The device of claim 1, wherein the first receiver unit is
compliant with system requirements for a receiver and the second
receiver unit is non-compliant with at least some of the system
requirements.
5. The device of claim 4, wherein the system requirements are
specified by a single-tone test and a two-tone test in IS-98D.
6. The device of claim 1, wherein the first frequency band is a
cellular band and the second frequency band is a Personal
Communication System (PCS) band.
7. The device of claim 1, wherein the second receiver unit is
further operable to receive, amplify, and downconvert a Global
Positioning System (GPS) signal and provide a downconverted GPS
signal.
8. The device of claim 1, wherein the first, second, and third
input signals are from one antenna.
9. The device of claim 1, further comprising: a detector operative
to detect for presence of large amplitude undesired signals in the
first or second input signal; and a control unit operative to
enable the first receiver unit if large amplitude undesired signals
are detected and enable the second receiver unit if large amplitude
undesired signals are not detected.
10. The device of claim 1, wherein the first and second input
signals are from a first antenna and the third input signal is from
a second antenna, and wherein the first receiver unit is for a
primary path and the second receiver unit is for a diversity
path.
11. The device of claim 10, wherein the second receiver unit is
enabled for a diversity mode with signals from the first and second
antennas being processed concurrently.
12. The device of claim 1, wherein the first and second receiver
units are operable to downconvert the first, second, and third
amplified signals directly from RF down to baseband.
13. The device of claim 1, wherein the second receiver unit is
biased with less current and occupies a smaller area than the first
receiver unit.
14. An integrated circuit comprising: a first receiver unit
including a first amplifier operable to receive and amplify a first
input signal for a first frequency band and provide a first
amplified signal, a second amplifier operable to receive and
amplify a second input signal for a second frequency band and
provide a second amplified signal, a first downconverter operable
to frequency downconvert the first amplified signal and provide a
first baseband signal, and a second downconverter operable to
frequency downconvert the second amplified signal and provide a
second baseband signal; and a second receiver unit including a
third amplifier operable to receive and amplify a third input
signal for the first or second frequency band and provide a third
amplified signal, and a third downconverter operable to frequency
downconvert the third amplified signal and provide a third baseband
signal, wherein the third amplifier and third downconverter are
wideband and are shared by the first and second frequency
bands.
15. The integrated circuit of claim 14, wherein the first receiver
unit is compliant with system requirements for a receiver and the
second receiver unit is non-compliant with the system
requirements.
16. The integrated circuit of claim 14, wherein the first and
second input signals are from a first antenna and the third input
signal is from a second antenna.
17. The integrated circuit of claim 14, wherein the first amplifier
and the first downconverter are narrowband and cover the first
frequency band, and wherein the second amplifier and the second
downconverter are narrowband and cover the second frequency
band.
18. The integrated circuit of claim 14, wherein the third amplifier
is further operable to receive and amplify a Global Positioning
System (GPS) signal and provide an amplified GPS signal, and
wherein the third downconverter is further operable to frequency
downconvert the amplified GPS signal and provide a GPS baseband
signal.
19. The integrated circuit of claim 14, wherein the second receiver
unit further includes a suppression unit operable to receive a
first input signal for the first frequency band, suppress a first
transmit signal component in the first input signal, and provide
the third input signal having the first transmit signal component
suppressed.
20. The integrated circuit of claim 19, wherein the suppression
unit is further operable to receive a second input signal for the
second frequency band, suppress a second transmit signal component
in the second input signal, and provide the third input signal
having the second transmit signal component suppressed.
21. The integrated circuit of claim 14, wherein the first receiver
unit further includes a first lowpass filter operable to filter the
first or second baseband signal and provide a first filtered
signal, and wherein the second receiver unit further includes a
second lowpass filter operable to filter the third baseband signal
and provide a second filtered signal.
22. The integrated circuit of claim 21, wherein the second lowpass
filter has a lower order than the first lowpass filter.
23. The integrated circuit of claim 21, wherein the second lowpass
filter has lower dynamic range and lower power consumption than the
first lowpass filter.
24. The integrated circuit of claim 14, wherein the third amplifier
and the third downconverter are biased with less current than the
first amplifier and the first downconverter, respectively.
25. The integrated circuit of claim 14, wherein the third amplifier
and the third downconverter are implemented with smaller-sized
circuit components than the first amplifier and the first
downconverter, respectively.
26. The integrated circuit of claim 14, further comprising: a first
local oscillator (LO) generator operable to provide a first LO
signal for the first and second downconverters, wherein the first
LO generator covers the first and second frequency bands; and a
second LO generator operable to provide a second LO signal for the
third downconverter, wherein the second LO generator also covers
the first and second frequency bands.
27. The integrated circuit of claim 26, wherein the first LO
generator has better phase noise performance than the second LO
generator.
28. The integrated circuit of claim 14, further comprising: a local
oscillator (LO) generator operable to provide an LO signal for the
first, second, and third downconverters, wherein the LO generator
covers the first and second frequency bands.
29. An apparatus comprising: means for receiving and amplifying a
first input signal for a first frequency band to obtain a first
amplified signal; means for receiving and amplifying a second input
signal for a second frequency band to obtain a second amplified
signal; means for downconverting the first amplified signal from
radio frequency (RF) to baseband to provide a first baseband
signal; means for downconverting the second amplified signal from
RF to baseband to provide a second baseband signal; means for
receiving and amplifying a third input signal for the first or
second frequency band to obtain a third amplified signal; and means
for downconverting the third amplified signal from RF to baseband
to provide a third baseband signal, wherein the means for receiving
and amplifying a third input signal and the means for
downconverting the third amplified signal include at least one RF
circuit block that is shared by the first and second frequency
bands.
30. The apparatus of claim 29, wherein the first and second
baseband signals are compliant with system requirements for a
receiver and the third baseband signal is non-compliant with the
system requirements.
31. A method of operating multiple receiver units in a wireless
device, comprising: detecting for presence of large amplitude
undesired signals in a first input signal or a second input signal;
enabling a first receiver unit to process the first input signal if
large amplitude undesired signals are detected; and enabling a
second receiver unit to process the second input signal if large
amplitude undesired signals are not detected, wherein the first
receiver unit includes at least two receive paths for at least two
frequency bands, and wherein the second receiver unit includes one
receive path for the at least two frequency bands.
32. The method of claim 31, wherein the first, second, and third
input signals are from one antenna.
33. The method of claim 31, wherein the first and second input
signals are from a first antenna and the third input signal is from
a second antenna.
Description
BACKGROUND
[0001] I. Field
[0002] The present invention relates generally to electronics, and
more specifically to a diversity receiver for wireless
communication.
[0003] II. Background
[0004] In a wireless communication system, a transmitter modulates
data onto a radio frequency (RF) carrier signal to generate an RF
modulated signal that is more suitable for transmission. The
transmitter then transmits the RF modulated signal via a wireless
channel to a receiver. The transmitted signal may reach the
receiver via one or more propagation paths (e.g., a line-of-sight
path and/or reflected paths). The characteristics of the
propagation paths may vary over time due to various phenomena such
as fading and multipath. Consequently, the transmitted signal may
experience different channel conditions and may be received with
different amplitudes and/or phases over time.
[0005] To provide diversity against deleterious path effects,
multiple antennas may be used to receive the RF modulated signal.
At least one propagation path typically exists between the transmit
antenna and each of the receive antennas. If the propagation paths
for different receive antennas are independent, which is generally
true to at least an extent, then diversity increases and the
received signal quality improves when multiple antennas are used to
receive the RF modulated signal.
[0006] A multi-antenna receiver conventionally has one RF receiver
processing path (or simply, "receive path") for each frequency band
and each receive antenna. For example, if the multi-antenna
receiver is designed to operate at two frequency bands (e.g.,
cellular and PCS bands), then it would normally have four receive
paths for the two frequency bands for each of the two receive
antennas. Each receive path includes various circuit blocks (e.g.,
amplifiers, filters, mixers, and so on) used to condition and
process a received signal at a designated frequency band from an
associated antenna. The circuit blocks are typically designed to
meet various system requirements such as linearity, dynamic range,
sensitivity, out-of-band rejection, and so on, as is known in the
art. In conventional receiver designs, the receive path is often
replicated for each frequency band of each of the receive antennas,
with circuit modifications (as needed) for different frequency
bands. The replication of the receive path circuitry results in
higher cost, larger area, and higher power consumption for the
multi-antenna receiver, all of which are undesirable. There is
therefore a need in the art for a low-cost diversity receiver.
SUMMARY
[0007] A low-cost diversity receiver having good performance is
described herein. The diversity receiver includes two (or possibly
more) receiver units. The first receiver unit is for a primary path
and is compliant with applicable system requirements (e.g., IS-98D,
cdma2000, and/or 3GPP requirements). The second receiver unit is
for a secondary/diversity path and has a receive path that is
shared by two or more frequency bands (e.g., cellular, PCS, GPS,
and so on). This shared design requires fewer circuit components to
support multiple frequency bands, reduces power consumption, and
lowers costs. Furthermore, the second receiver unit is not fully
compliant with all of the system requirements. For example, the
second receiver unit may be designed to operate over a smaller
dynamic range and to meet requirements for sensitivity but not for
out-of-band rejection of large amplitude "jammers", which are
undesired signals of a particular level or higher. This
non-compliant design allows the second receiver unit to be
implemented with lower power consumption, less area, and lower
cost. The second receiver unit can provide good performance under
most operating conditions. For a multi-antenna receiver, the two
receiver units can be used to simultaneously process two input
signals from two antennas. For a single-antenna receiver, one of
the two receiver units may be selected, based on the operating
conditions, to process a single input signal from one antenna.
[0008] In an exemplary embodiment, a dual-band, dual-path receiver
with two receiver units is described. Each receiver unit can
operate at one of two frequency bands. The first receiver unit
includes first and second amplifiers, first and second
downconverters, and a first lowpass filter. The first amplifier
amplifies a first input signal for a first frequency band (e.g.,
cellular band) and provides a first amplified signal. The first
downconverter translates the first amplified signal in frequency
(e.g., from RF down to baseband) and provides a first baseband
signal. The second amplifier amplifies a second input signal for a
second frequency band (e.g., PCS band) and provides a second
amplified signal. The second downconverter translates the second
amplified signal in frequency and provides a second baseband
signal. The first lowpass filter filters the first or second
baseband signal and provides a first filtered signal.
[0009] The second receiver unit includes a third amplifier, a third
downconverter, and a second lowpass filter. The third amplifier
amplifies a third input signal for the first or second frequency
band and provides a third amplified signal. The third downconverter
translates the third amplified signal down in frequency and
provides a third baseband signal. The second lowpass filter filters
the third baseband signal and provides a second filtered signal.
The first amplifier and first downconverter are narrowband and
cover the first frequency band. The second amplifier and second
downconverter are also narrowband and cover the second frequency
band. The third amplifier and third downconverter are wideband,
cover the first and second frequency bands, and are shared by these
two frequency bands.
[0010] Various aspects and embodiments of the invention are
described in further detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The features and nature of the present invention will become
more apparent from the detailed description set forth below when
taken in conjunction with the drawings in which like reference
characters identify correspondingly throughout and wherein:
[0012] FIG. 1 shows a wireless communication system;
[0013] FIG. 2 shows a single-antenna terminal;
[0014] FIG. 3 shows a multi-antenna terminal;
[0015] FIG. 4 shows a single-band, dual-path receiver;
[0016] FIG. 4 shows a dual-band, dual-path receiver;
[0017] FIG. 5 shows a dual-band, dual-path plus GPS receiver;
[0018] FIG. 6 shows a dual-band, dual-path plus GPS receiver with a
shared local oscillator (LO) generator;
[0019] FIG. 7 shows frequency responses of filters within receiver
units in FIG. 4;
[0020] FIG. 8 shows a jammer detector; and
[0021] FIG. 9 shows a process for operating two receiver units in a
wireless terminal.
DETAILED DESCRIPTION
[0022] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment or design
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other embodiments or designs.
[0023] FIG. 1 shows a wireless communication system 100 in which a
number of wireless terminals communicate with a number of base
stations. For simplicity, only two terminals 110a and 10b and two
base stations 120a and 120b are shown in FIG. 1. A terminal may
also be referred to as a remote station, a mobile station, an
access terminal, a user equipment (UE), a wireless communication
device, a cellular phone, or some other terminology. Terminal 110a
is equipped with a single antenna, and terminal 110b is equipped
with two antennas. A base station is a fixed station and may also
be referred to as an access point, a Node B, or some other
terminology. A mobile switching center (MSC) 140 couples to the
base stations and provides coordination and control for these base
stations.
[0024] A terminal may or may not be capable of receiving signals
from satellites 130. Satellites 130 may belong to a satellite
positioning system such as the well-known Global Positioning System
(GPS). Each GPS satellite transmits a GPS signal encoded with
information that allows GPS receivers on earth to measure the time
of arrival of the GPS signal. Measurements for a sufficient number
of GPS satellites can be used to accurately estimate a
three-dimensional position of a GPS receiver. A terminal may also
be capable of receiving signals from other types of transmitting
sources such as a Bluetooth transmitter, a Wireless Fidelity
(Wi-Fi) transmitter, a wireless local area network (WLAN)
transmitter, an IEEE 802.11 transmitter, and so on.
[0025] In FIG. 1, each terminal 110 is shown as receiving signals
from multiple transmitting sources simultaneously, where a
transmitting source may be a base station or a satellite. In
general, a terminal may receive signals from zero, one, or multiple
transmitting sources at any given moment. For multi-antenna
terminal 110b, the signal from each transmitting source is received
by each of the multiple antennas at the terminal, albeit at
different amplitudes and/or phases.
[0026] System 100 may be a Code Division Multiple Access (CDMA)
system, a Time Division Multiple Access (TDMA) system, or some
other wireless communication system. A CDMA system may implement
one or more CDMA standards such as IS-95, IS-2000 (also commonly
known as "1x"), IS-856 (also commonly known as "1xEV-DO"),
Wideband-CDMA (W-CDMA), and so on. A TDMA system may implement one
or more TDMA standards such as Global System for Mobile
Communications (GSM). The W-CDMA standard is defined by a
consortium known as 3GPP, and the IS-2000 and IS-856 standards are
defined by a consortium known as 3GPP2. These standards are known
in the art.
[0027] System 100 operates on one or more specific frequency bands.
Table 1 lists various frequency bands in which system 100 may
operate, as well as the frequency band for GPS.
1TABLE 1 Frequency Band Frequency Range Personal Communication
System (PCS) 1850 to 1990 MHz Cellular 824 to 894 MHz Digital
Cellular System (DCS) 1710 to 1880 MHz GSM900 890 to 960 MHz
International Mobile Telecommunications- 1920 to 2170 MHz 2000
(IMT-2000) CDMA450 411 to 493 MHz JCDMA 832 to 925 MHz KPCS 1750 to
1870 MHz GPS 1574.4 to 1576.4 MHz
[0028] The PCS band is also known as GSM1900, the DCS band is also
known as GSM1800, and the cellular band is also known as an
Advanced Mobile Phone System (AMPS) band. System 100 may also
operate on a frequency band that is not listed in Table 1.
[0029] For each of the frequency bands listed in Table 1 (except
for GPS), one frequency range is used for the forward link (i.e.,
downlink) from the base stations to the terminals, and another
frequency range is used for the reverse link (i.e., uplink) from
the terminals to the base stations. As an example, for the cellular
band, the 824 to 849 MHz range is used for the reverse link, and
the 869 to 894 MHz range is used for the forward link.
[0030] A terminal may be a single-band terminal or a multi-band
terminal. A single-band terminal supports operation on one specific
frequency band (e.g., cellular or PCS). A multi-band terminal
supports operation on multiple frequency bands (e.g., cellular and
PCS) and typically operates on one of the supported bands at any
given moment. A multi-band terminal can communicate with different
wireless communication systems operating on different frequency
bands.
[0031] Low-cost receivers that can provide good performance are
described herein. These receivers may be used for (1) terminals
with single or multiple antennas, (2) terminals supporting multiple
frequency bands, and (3) terminals with or without GPS capability.
Some exemplary receivers are described below.
[0032] FIG. 2 shows a block diagram of an embodiment of
single-antenna terminal 110a. In this embodiment, terminal 110a
includes a single antenna 212 and two receiver units 220a and 220b
for two receive paths. Antenna 212 receives RF modulated signals
from base stations 120 and/or satellites 130 and provides a
received signal that includes versions of the RF modulated signals
from these transmitting sources. Each receiver unit 220 processes
the received signal from antenna 212 and provides a respective
output baseband signal. Receiver unit 220a is designated as the
primary path, is designed to meet applicable system requirements
(e.g., for linearity, dynamic range, sensitivity, out-of-band
rejection, and so on), and may be used for all operating
conditions. Receiver unit 220b is designated as the secondary path,
is wideband and designed based on less stringent requirements, and
may be used for most operating conditions. Exemplary designs for
receiver units 220a and 220b are described below.
[0033] A switch (SW) 230 receives the two output baseband signals
(Pout and Sout) from receiver units 220a and 220b, selects one of
the two signals based on a Sel signal, and provides the selected
output baseband signal to an analog-to-digital converter (ADC)
240a. ADC 240a digitizes the selected output baseband signal and
provides a first stream of data samples to a digital signal
processor (DSP) 250 for further processing. An ADC 240b receives
and digitizes the output baseband signal from receiver unit 220b
and provides a second stream of data samples to DSP 250. Although
not shown in FIG. 2 for simplicity, each output baseband signal and
each data sample stream may be a complex signal/stream having an
inphase (I) component and a quadrature (Q) component.
[0034] For the embodiment shown in FIG. 2, a jammer detector 260
receives a first detector input signal (D1) from receiver unit 220a
and a second detector input signal (D2) from receiver unit 220b,
detects for the presence of large amplitude jammers in the received
signal, and provides a jammer status signal indicating whether
large amplitude jammers are present in the received signal. A
control unit 262 receives the jammer status signal from jammer
detector 260 and a Mode signal from DSP 250, which indicates the
operating mode of terminal 110a. Control unit 262 provides the Enb1
and Enb2 signals used to enable receiver units 220a and 220b,
respectively, and the Sel signal used by switch 230 to select one
of the two output baseband signals. For example, control unit 262
may select (1) receiver unit 220a if large amplitude jammers are
detected in the received signal and (2) receiver unit 220b
otherwise. Control unit 262 may also enable both receiver units
220a and 220b if signals from two systems (e.g., wireless cellular
and GPS) are to be processed simultaneously.
[0035] In one configuration, either receiver unit 220a or 220b is
selected for use at any given moment, depending on the operating
conditions. For this configuration, ADC 240b may be omitted since
only one system needs to be processed at any given moment. In
another configuration, both receiver units 220a and 220b may be
active at the same time to simultaneously process signals from two
different systems (e.g., wireless cellular and GPS). For this
configuration, switch 230 may be omitted and receiver units 220a
and 220b may provide their output baseband signals directly to ADCs
240a and 240b, respectively.
[0036] FIG. 3 shows a block diagram of an embodiment of
multi-antenna terminal 110b. In this embodiment, terminal 110b
includes two antenna 312a and 312b and two receiver units 320a and
320b. The two antennas 312a and 312b may be formed in various
manners at terminal 110b (e.g., with printed traces on a circuit
board, wire conductors, and so on), as is known in the art. Each
receiver unit 320 processes the received signal from one antenna
312 and provides a respective output baseband signal. Receiver unit
320a is designated as the primary path, is designed to meet
applicable system requirements, and may be used for all operating
conditions. Receiver unit 320b is designated as the
secondary/diversity path, is wideband and designed based on less
stringent requirements, and may be used for most operating
conditions. In one configuration, either receiver unit 320a or 320b
is selected for use at any given moment, depending on the operating
conditions. In another configuration, both receiver units 320a and
320b may be active at the same time to simultaneously process two
received signals for the same wireless system, to achieve
diversity. In yet another configuration, both receiver units 320a
and 320b may simultaneously process signals for two different
systems (e.g., wireless cellular and GPS). Exemplary designs for
receiver units 320a and 320b are described below.
[0037] ADC 340a receives and digitizes the first output baseband
signal (Pout) from receiver unit 320a and provides a first data
sample stream to a DSP 350. An ADC 340b receives and digitizes the
second output baseband signal (Sout) from receiver unit 320b and
provides a second data sample stream to DSP 350. A jammer detector
360 detects for the presence of large amplitude jammers in the
first and/or second received signal and provides a jammer status
signal. A control unit 362 enables one or both receiver units 320a
and 320b based on the jammer status signal from jammer detector 360
and the Mode signal from DSP 350.
[0038] FIG. 4 shows a block diagram of a dual-band, dual-path
receiver 400, which may be used for both single-antenna terminal
110a and multi-antenna terminal 10b. Receiver 400 includes two
receiver units 420a and 420b that may be used for receiver units
220a and 220b, respectively, in FIG. 2. In this case, both receiver
units 420 are provided with the same received signal from antenna
212. Receiver units 420a and 420b may also be used for receiver
units 320a and 320b, respectively, in FIG. 3. In this case,
receiver units 420a and 420b are provided with different received
signals from antennas 312a and 312b, respectively. Each receiver
unit 420 supports operation on two frequency bands. For clarity,
the description below is for the cellular and PCS bands. Receiver
unit 420a is designated as the primary path, and receiver unit 420b
is designated as the secondary/diversity path. The input signal for
receiver unit 420a is referred to as the primary path input signal
(Pin), and the input signal for receiver unit 420b is referred to
as the secondary path input signal (Sin).
[0039] A receiver may implement a super-heterodyne architecture or
a direct-to-baseband architecture. In the super-heterodyne
architecture, the received signal is frequency downconverted in
multiple stages, e.g., from RF to an intermediate frequency (IF) in
one stage, and then from IF to baseband in another stage. In the
direct-to-baseband architecture, the received signal is frequency
downconverted from RF directly to baseband in one stage. The
super-heterodyne and direct-to-baseband architectures may use
different circuit blocks and/or have different circuit
requirements. For clarity, the following description is for the
direct-to-baseband architecture.
[0040] Receiver unit 420a is designed to meet applicable system
requirements. For CDMA, IS-98D and cdma2000 specify a two-tone test
and a single-tone test. For the two-tone test, two tones (or
jammers) are located at +900 KHz and +1700 KHz from the center
frequency of a CDMA waveform and are 58 dB higher in amplitude than
the CDMA signal level. For the single-tone test, a single tone is
located at +900 KHz from the center frequency of the CDMA waveform
and is 72 dB higher in amplitude than the CDMA signal level. These
tests define the linearity and dynamic range requirements for the
receive path. In most systems, jammers are present for only a small
fraction of the time and rarely reach the +58 or +72 dB level as
specified by IS-98D and cdma2000. Nevertheless, receiver unit 420a
may be designed to be IS-98D and cdma2000 compliant so that they
can provide the specified performance for all operating conditions.
Receiver unit 420b may be designed based on less stringent
requirements. For example, receiver unit 420b may be designed to
meet dynamic range and sensitivity requirements, albeit with an
assumption that large amplitude jammers are not present in the
received signal. Receiver unit 420b can provide good performance
most of the time since large amplitude jammers are only present
intermittently.
[0041] Within receiver unit 420a for the primary path, a diplexer
422a receives the Pin signal, provides a first cellular signal to a
variable gain low noise amplifier (VG LNA) 424a, and provides a
first PCS signal to a variable gain LNA 424b. Variable gain LNA
424a amplifies the first cellular signal with a gain G1ca. A
bandpass filter (BPF) 426a filters the signal from LNA 424a to pass
signal components in the band of interest and remove out-of-band
noise and undesired signals. For two-way communication, signals are
transmitted simultaneously on the forward link and reverse link.
The transmit signal sent by the terminal on the reverse link is
typically much larger in amplitude than the received signal for the
forward link. Bandpass filter 426a may pass the RF components for
the entire receive frequency range (e.g., from 869 to 894 MHz for
the cellular band) and filter out and suppress the RF components
for the transmit frequency range (e.g., from 824 to 849 MHz for the
cellular band). Bandpass filter 426a thus has a passband that
corresponds to the entire frequency range/band of interest (e.g.,
cellular). Because of the potentially large difference in the
transmit and receive signal levels, bandpass filter 426a needs to
provide a large amount of out-of-band rejection in order to meet
system requirements. Bandpass filter 426a may be implemented with a
surface acoustic wave (SAW) filter, which has a sharp roll-off and
is commonly used for applications requiring large attenuation of
out-of-band signals.
[0042] A variable gain amplifier (VGA) 428a amplifies the signal
from bandpass filter 426a with a gain G1cb and provides a
conditioned cellular signal having the desired signal level. LNA
424a and VGA 428a provide the required amplification for the first
cellular signal, which may vary by 90 dB or more. (The total
required gain may be provided by LNA 424a, VGA 428a, and other
circuit blocks and units such as DSP 250 or 350.) A downconverter
430a receives and frequency downconverts the conditioned cellular
signal with a first LO signal (LO1) and provides a cellular
baseband signal, which is also used as the D1 signal for the jammer
detector. The frequency of the first LO signal is selected such
that the signal component in the RF channel of interest is
downconverted to baseband or near-baseband. For CDMA, each
frequency band covers many RF channels, and each RF channel has a
bandwidth of 1.23 MHz. A wireless terminal typically receives
signal on one RF channel at any given moment.
[0043] Similarly, the first PCS signal is amplified by variable
gain LNA 424b with a gain G1pa, filtered by a bandpass filter 426b,
and further amplified by a VGA 428b with a gain G1pb to obtain a
conditioned PCS signal. Bandpass filter 426b may also be
implemented with a SAW filter that passes the receive frequency
range for the PCS band (from 1930 to 1990 MHz) and filters out
other frequencies. For the direct-to-baseband architecture, each
bandpass filter 426 attenuates the signal components in the
transmit frequency range for the associated band. A downconverter
430b receives and frequency downconverts the conditioned PCS signal
with the first LO signal from LO generator 446a and provides a PCS
baseband signal.
[0044] A high-performance lowpass filter 440a then filters the
cellular baseband signal or the PCS baseband signal to pass the
signal components in the RF channel of interest and to remove noise
and undesired signals that may be generated by the downconversion
process. For the direct-to-baseband architecture, each bandpass
filter 426 may pass the entire frequency band of interest, and
lowpass filter 440a would then pass the RF channel of interest.
Lowpass filter 440a is designed to have a relatively sharp roll-off
in order to attenuate large amplitude jammers in the received
signal. These jammers can take up a large portion of the dynamic
range of the subsequent ADC if they are not sufficiently filtered.
Lowpass filter 440a may be implemented with various filter types
(e.g., Butterworth, elliptical, Chebychev, and so on), with the
proper filter order and bandwidth, and with sufficient bias current
to meet linearity and dynamic range requirements. For example,
lowpass filter 440a may be implemented with a 5th order elliptical
filter. Lowpass filter 440a provides a first filtered cellular/PCS
baseband signal. An amplifier 442a amplifies and buffers the first
filtered cellular/PCS baseband signal and provides a first output
cellular/PCS baseband signal (Pout).
[0045] An LO generator 446a provides the first LO signal used to
downconvert the Pin signal. LO generator 446a may be implemented
with a voltage controlled oscillator (VCO) or some other type of
oscillator. For example, LO generator 446a may be implemented with
a dual-band VCO that can provide the first LO signal with the
proper frequency, depending on whether the cellular or PCS band is
selected. The dual-band VCO may be designed to span a frequency
range of 3.3 to 4.4 GHz, which covers four times the lowest
frequency in the cellular band and twice the highest frequency in
the PCS band. The frequency of the first LO signal is selected such
that the signal component in the RF channel of interest in the
selected frequency band is downconverted to baseband or
near-baseband. A phase locked loop (PLL) 448a receives the first LO
signal and generates a first control signal for LO generator 446a
such that the frequency and/or phase of the first LO signal is
locked to a reference signal (not shown in FIG. 4).
[0046] Within receiver unit 420b for the secondary/diversity path,
a diplexer 422b receives the Sin signal, provides a second cellular
signal to a variable gain LNA 424c, and provides a second PCS
signal to a variable gain LNA 424d. The second cellular signal is
amplified by variable gain VGA 424c with a gain G2c and processed
by a suppression unit 456. Similarly, the second PCS signal is
amplified by variable gain LNA 424d with a gain G2p and processed
by suppression unit 456. Suppression unit 456 suppresses large
amplitude undesired signal components in the signals from LNAs 424c
and 424d. A simple and low-cost design may be used for suppression
unit 456. For example, since the transmit signal is the predominant
undesired signal component, suppression unit 456 may be implemented
with a transmit cancellation unit (which is also called an adaptive
filter) described in commonly assigned U.S. patent application Ser.
No. ______ [Attorney Docket No. 020181], entitled "Adaptive Filter
for Transmit Signal Rejection," filed xx. This transmit
cancellation unit receives a portion of the transmit signal (TXin),
adjusts the gain and/or phase of this TXin signal, and subtracts
the adjusted signal to suppress the transmit signal component in
the Sin signal. Suppression unit 456 may also be implemented with a
bandpass filter, a highpass filter, a ceramic filter, and so
on.
[0047] A multiplexer (MUX) 458 selects either the filtered cellular
signal or the filtered PCS signal from suppression unit 456,
depending on the selected frequency band. A VGA 428c amplifies the
selected signal from suppression unit 456 with a gain G2 and
provides a conditioned cellular or PCS signal, depending on the
selected frequency band. Multiplexer 458 symbolically shows the
selection of one of the two bands. The band selection can be
implemented in various manners. For example, two VGAs 428 coupled
together may be used for the two bands, the VGA for the selected
band may be enabled, and the other VGA may be disabled.
[0048] A downconverter 430c receives and frequency downconverts the
conditioned cellular/PCS signal with a second LO signal (LO2) from
an LO generator 446b and provides a cellular/PCS baseband signal,
which is also used as the D2 signal for the jammer detector. The
frequency of the second LO signal is selected such that the signal
component in the RF channel of interest in the selected frequency
band is downconverted to baseband or near-baseband. A
low-performance lowpass filter 440b then filters the cellular/PCS
baseband signal to pass the signal components in the RF channel of
interest and to remove noise and undesired signals. Filter 440b may
be implemented with lower order, less bias current, smaller size,
and so on, than for filter 440a. This is because the requirements
for filter 440b are less stringent than those for filter 440a. For
example, filter 440b may be implemented with a 3rd order elliptical
filter having more gradual attenuation than filter 440a. Filter
440b provides a second filtered cellular/PCS baseband signal. An
amplifier 442b amplifies and buffers the second filtered
cellular/PCS baseband signal and provides a second output
cellular/PCS baseband signal (Sout).
[0049] An LO generator 446b provides the second LO signal used to
downconvert the Sin signal. LO generator 446b may be implemented
with a dual-band VCO, similar to LO generator 446a. However, LO
generator 446b may be designed with more relaxed phase noise
requirements. A PLL 448b receives the second LO signal and
generates a second control signal for LO generator 446b. The same
or different reference signals may be used for PLLs 448a and
448b.
[0050] Receiver unit 420a is designed to be compliant with
applicable system requirements for both frequency bands. To meet
these requirements, two separate receive paths are typically needed
from diplexer 422a to lowpass filter 440a. Each of the two receive
paths is designed for (or tuned to) the frequency band of interest
in order to meet linearity, dynamic range, and sensitivity
requirements. Two separate narrowband LNAs 424a and 424b are used
for the two frequency bands and are designed for low noise figure,
which typically requires narrowband matching at the frequency band
of interest. Two separate narrowband VGAs 428a and 428b and two
separate narrowband downconverters 430a and 430b are also typically
used to achieve the desired linearity over a wide dynamic range.
The narrowband circuit blocks may use tuned circuits, inductive
degeneration, and other circuit techniques known in the art to
achieve the desired performance. LO generator 446a is designed to
have good phase noise performance. Good performance for these
circuit blocks typically requires the use of larger-sized circuit
components (e.g., larger capacitors, inductors and/or transistors)
and large amounts of bias current.
[0051] Receiver unit 420b is designed to meet less stringent
requirements, which assume that large amplitude jammers are not
present. Receiver unit 420b can be designed for lower cost, lower
power consumption, and smaller area than receiver unit 420a.
Suppression unit 456 may be implemented with on-chip circuit
components instead of with an external SAW filter (which may be
needed for bandpass filters 426a and 426b). Separate narrowband
LNAs 424c and 424d are used for the two frequency bands to attain
low noise figures. However, these LNAs are typically small in size
and consume small amount of bias current. Wideband VGA 428c and
wideband downconverter 430c are shared by both frequency bands and
can be implemented without using inductors (which typically occupy
a large area) or using inductors of lower quality. Because of the
less stringent linearity and dynamic range requirements, LNA 424c
and 424d, VGA 428c, downconverter 430c, filter 440b, and amplifier
442b may be designed with smaller-sized circuit components (e.g.,
smaller capacitors) and less bias current. Also, because large
amplitude jammers are assumed to be absent for receiver unit 420b,
the overall gain may be distributed differently for the
secondary/diversity path in a manner to further achieve low cost,
low power, and small area.
[0052] FIG. 4 shows a specific design for receiver units 420a and
420b. In general, a receiver unit may perform signal conditioning
using one or more stages of amplifier, filter, mixer, and so on,
which may be arranged differently from that shown in FIG. 4.
Moreover, a receiver unit may employ other circuit blocks not shown
in FIG. 4 for signal conditioning.
[0053] FIG. 7 shows the frequency responses of various filters
within receiver units 420a and 420b. Bandpass filter 426a has a
frequency response 726, which is characterized by a passband that
spans the entire frequency range/band of interest (e.g., cellular
or PCS) and a sharp roll-off. Suppression unit 456 has a frequency
response 756 that also passes the signal components in the
frequency range/band of interest and suppresses the transmit
signal. For simplicity, the frequency response of suppression unit
456 is represented as a notch filter in FIG. 7. High-performance
lowpass filter 440a has a frequency response 740a, which is
characterized by a passband for one RF channel and a relatively
sharp roll-off. Low-performance lowpass filter 440b has a frequency
response 740b, which is characterized by a passband for one RF
channel and a more gradual roll-off.
[0054] A receiver may also be designed to support more than two
frequency bands based on the concept described above for receiver
400.
[0055] FIG. 5 shows a block diagram of a dual-band plus GPS,
dual-path receiver 500. Receiver 500 includes two receiver units
520a and 520b that may be used for receiver units 220a and 220b,
respectively, of single-antenna terminal 110a in FIG. 2, and for
receiver units 320a and 320b, respectively, of multi-antenna
terminal 110b in FIG. 3. Each receiver unit 520 supports operation
on two frequency bands. Receiver unit 520b has a receive path that
is shared by both frequency bands plus GPS.
[0056] Receiver unit 520a for the primary path is similar in design
to receiver unit 420a in FIG. 4. However, FIG. 5 shows a quadrature
design for downconverters 530a and 530b and the subsequent baseband
circuit blocks. Within each downconverter 530, a mixer 532 receives
and downconverts the conditioned signal from an associated VGA 528
with an inphase first LO signal (ILO1) from a divider unit 536 and
provides an inphase (I) baseband signal. Similarly, a mixer 534
receives and downconverts the conditioned signal from the same VGA
528 with a quadrature first LO signal (QLO1) from divider unit 536
and provides a quadrature (Q) baseband signal. The I and Q baseband
signals (from both downconverters 530a and 530b) are filtered by
high-performance lowpass filters 540a and 540b, respectively, and
further amplified by amplifiers 542a and 542b, respectively, to
obtain output I and Q cellular/PCS baseband signals (Pout,i and
Pout,q).
[0057] Receiver unit 520b for the secondary/diversity path is
similar in design to receiver unit 420b in FIG. 4. However,
receiver unit 520b includes three front-end paths for cellular,
PCS, and GPS. The front-end paths for the cellular and PCS are
implemented with a diplexer 522b, variable gain VGAs 524c and 524d,
a suppression unit 556, and a multiplexer 558. These circuit blocks
operate as described above for receiver unit 420b. For the third
front-end path for GPS, a GPS signal (Gin) is amplified by a
variable gain LNA 524e with a gain G2g and filtered by a bandpass
filter 526c. Bandpass filter 526c may be implemented with a SAW
filter or some other type of filter. Multiplexer 558 selects the
cellular, PCS, or GPS signal, depending on the selected
system/band. A VGA 528c amplifies the signal from multiplexer 558
with a gain G2 and provides a conditioned cellular, PCS, or GPS
signal, depending on which one of the three receive paths is
selected.
[0058] FIG. 5 also shows a quadrature design for frequency
downconverter 530c and the subsequent baseband circuit blocks for
the secondary/diversity path. Downconverter 530c is implemented
with mixers 532c and 534c and a divider unit 536c, which operate as
described above for downconverters 530a and 530b. Downconverter
530c performs quadrature downconversion of the conditioned
cellular/PCS/GPS signal from VGA 528c and provides I and Q baseband
signals, which are filtered by low-performance lowpass filters 540c
and 540d, respectively, and further amplified by amplifiers 542c
and 542d, respectively, to obtain output I and Q cellular/PCS/GPS
baseband signals (Sout,i and Sout,q).
[0059] LO generator 546b may be implemented with a VCO that can
span a frequency range of 3.15 to 4.4 GHz, which covers four times
the cellular band, twice the PCS band, and twice the GPS band. LO
generator 546b may be designed with more relaxed phase noise
requirements than LO generator 546a.
[0060] Receiver unit 520b is wideband and designed for lower cost,
lower power consumption, and smaller area than receiver unit 520a.
Wideband VGA 528c and wideband downconverter 530c are shared for
both frequency bands and GPS.
[0061] Receivers 400 and 500 each include two LO generators that
can be operated independently. Moreover, each of the two LO
generators covers all of the frequency bands of interest. This
design allows the primary and secondary paths to simultaneously
process two signals on two different RF channels. This capability
may be useful for various applications. For example, a terminal
with this capability can receive two simultaneous transmissions on
two RF channels from one or two systems. As another example, the
terminal with this capability can perform mobile-assisted hand-off
(MAHO) to select the best base stations to communicate with. The
terminal can receive a transmission from a serving base station
with the primary path and can simultaneously search for signals
from other base stations with the secondary/diversity path. This
would then allow the terminal to initiate a hand-off to another
base station that is better than the serving base station, if one
is found. If independent operation of the primary and secondary
paths is not needed, then one LO generator can be shared by the
primary and secondary paths.
[0062] FIG. 6 shows a block diagram of a dual-band plus GPS,
dual-path receiver 600 with a shared LO generator. Receiver 600
includes two receiver units 620a and 620b that may be used for
receiver units 220a and 220b, respectively, of single-antenna
terminal 110a in FIG. 2, and for receiver units 320a and 320b,
respectively, of multi-antenna terminal 110b in FIG. 3. Receiver
unit 620a is for the primary path and is implemented in the same
manner as receiver unit 520a in FIG. 5.
[0063] Receiver unit 620b is for the secondary/diversity path and
is implemented in similar manner as receiver unit 520b in FIG. 5.
Receiver unit 620b further includes a multiplexer 638 that receives
the first LO signal from an LO generator 646a and the second LO
signal from an LO generator 646b, provides the first LO signal to a
downconverter 630c if the cellular or PCS band is selected, and
provides the second LO signal if GPS is selected. LO generator 646a
may be implemented with a VCO that can span a frequency range of
3.3 to 4.4 GHz, which covers four times the cellular band and twice
the PCS band. LO generator 646b may be implemented with a VCO that
covers 3.15 GHz, which is twice the GPS band. The design for LO
generator 646b and PLL 648b can be simplified if they are required
to cover only GPS (instead of GPS, cellular, and PCS).
[0064] FIG. 8 shows a block diagram of a jammer detector 860, which
may be used for jammer detectors 260 and 360 in FIGS. 2 and 3. The
D1 and D2 signals from the first and second receiver units are
rectified by rectifiers 862a and 862b, filtered by lowpass filters
864a and 864b, and provided to comparators 866a and 866b,
respectively. Each rectifier 862 converts its input signal from a
sinusoidal signal (with positive and negative amplitude) to a
single-ended signal (with only positive amplitude) and may be
implemented with a diode. Each lowpass filter 864 may be
implemented, for example, with a single-order lowpass filter of an
appropriate bandwidth (e.g., several hundred Hertz). Each
comparator 866 compares its filtered signal against a threshold
level (Vth) and provides an output signal, which is (1) logic high
(`1`) if the filtered signal amplitude is larger than the threshold
level, indicating the presence of large amplitude jammers in the
received signal, and (2) logic low (`0`) otherwise. Detector logic
868 combines the output signals of comparators 866a and 866b and
provides the jammer status signal to control unit 262 or 362.
[0065] In general, jammer detection may be performed based on (1)
only the D1 signal, (2) only the D2 signal, or (3) both the D1 and
D2 signals. The filtered signals may be compared against the
threshold level as shown in FIG. 8 to obtain a 1-bit output signal.
The jammer status signal from jammer detector 860 may be used to
enable or disable each of the two receiver units. The filtered
signals from lowpass filters 864a and 864b may also be digitized
with an ADC to obtain multiple bits of resolution. The circuit
blocks in the two receiver units may be adjusted (e.g., with
different gains, bias currents, and so on) based on whether or not
large amplitude jammers are detected and/or the specific signal
level of the jammers.
[0066] FIG. 9 shows a flow diagram of a process 900 for operating
two receiver units in a wireless terminal. The presence of large
amplitude jammers in a first input signal or a second input signal
is detected (block 912). The first and second input signals may be
from (1) one antenna for a single-antenna terminal or (2) two
antennas for a multi-antenna terminal. The first receiver unit
(which is spec-compliant, e.g., IS-98D compliant) is enabled to
process the first input signal if large amplitude jammers are
detected (block 914). The second receiver unit (which is not fully
spec-compliant) is enabled to process the second input signal if
large amplitude jammers are not detected (block 916). The first and
second receiver units may both be enabled if the multi-antenna
terminal is operating in a diversity mode and the received signals
from both antennas are to be processed simultaneously. Electrical
characteristics (e.g., gains, bias currents, and so on) of the
circuit blocks in the enabled receiver unit(s) may be adjusted
based on the detected jammer signal level and/or the desired signal
level (block 918).
[0067] For simplicity, the description above is for a
direct-to-baseband architecture. The concepts described herein may
also be used for a super-heterodyne architecture. In this case, for
the primary path, one variable gain LNA and one RF to IF
downconverter may be provided for each frequency band. The input
signal for each frequency band is downconverted to a predetermined
IF and filtered with a common bandpass filter. The bandpass filter
may be implemented with a SAW filter and may perform RF channel
selection (i.e., has a passband corresponding to one RF channel,
instead of an entire frequency band). Another downconverter then
frequency downconverts the IF signal to baseband. If the RF channel
selection is performed by the bandpass filter, then the
requirements for the lowpass filter may be relaxed. For the
secondary receive path, the circuit blocks may be designed based on
less stringent requirements, which assume the absence of large
amplitude jammers in the received signal.
[0068] The diversity receiver described herein may be used for a
wireless terminal to receive forward link transmissions from base
stations. The diversity receiver may also be used for a base
station to receive reverse link transmissions from user
terminals.
[0069] The diversity receiver described herein may be used for
various wireless communication systems such as a CDMA system, a
TDMA system, a GSM system, an AMPS system, a multiple-input
multiple-output (MIMO) system, an orthogonal frequency division
multiplexing (OFDM) system, an orthogonal frequency division
multiple access (OFDMA) system, a wireless local area network
(WLAN), and so on.
[0070] A large portion of a diversity receiver (possibly all
circuit blocks except SAW filters, control units 262 and 362, and
DSPs 250 and 350) may be implemented on one or more RF integrated
circuits (RFICs). The diversity receiver may also be fabricated
with various IC process technologies such as complementary metal
oxide semiconductor (CMOS), bipolar junction transistor (BJT),
bipolar-CMOS (BiCMOS), silicon germanium (SiGe), gallium arsenide
(GaAs), and so on.
[0071] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
* * * * *